Double Pipe Heat Exchanger and Method of Manufacturing the Same

ABSTRACT

A double pipe heat exchanger that can be produced easily and can be used as a part of piping by bending the whole body, wherein an inner pipe is configured so that: a plurality of balloon-shaped bulges communicating with one another and extending from the center toward the radial directions in a cross section orthogonal to the axis line thereof may be formed; the outer circumference of the bulges may be bent into the shape of waves in an axial cross section; and the top portions of the waves may touch the inner surface of an outer pipe. Then in the state, the whole body including the inner pipe and the outer pipe is bent by applying external force.

TECHNICAL FIELD

The present invention relates to a double pipe heat exchanger that is: used as an EGR cooler, an oil cooler, or the like; and bent along the piping route of a vehicle.

BACKGROUND ART

An EGR cooler is interposed in the middle of the pipe for the exhaust gas of an engine and cools the exhaust gas with cooling water. An example thereof is “a double pipe heat exchanger” disclosed in Japanese Unexamined Patent Publication No. 2000-161871.

The heat exchanger has a double pipe structure comprising an inner pipe and an outer pipe, and radiator fins are integrally bent and formed at an intermediate portion in the axial direction of the inner pipe. That is, a large number of protrusions are formed in the radial directions from the center in a cross section at the intermediate portion of the inner pipe.

A conventional EGR cooler is interposed into a linear part located in the middle of the exhaust gas pipe for an engine. As a result, the positioning of the EGR cooler is inflexible, the number of parts increases, and the production cost as a whole has been obliged to increase.

In view of the above situation, an object of the present invention is to provide: a double pipe heat exchanger that has a simple structure and can be easily bent along a piping route; and a method for producing the double pipe heat exchanger.

DISCLOSURE OF THE INVENTION

The present invention according to claim 1 is a double pipe heat exchanger wherein:

-   -   an outer pipe (2) is fitted outside an inner pipe (1);     -   in a cross section orthogonal to the axis line of the inner pipe         (1) , the inner pipe (1) has a plurality of balloon-shaped         bulges (3) communicating with one another and extending in the         radial directions from the center, and the width of each of the         bulges (3) is the largest at an intermediate portion between the         center and the outside of the inner pipe (1) in a radial         direction and gradually decreases toward both the sides of the         bulge (3) in the radial direction;     -   a plurality of grooves (10) is formed on the outer surface side         at the center portion of the inner pipe (1) in the manner of         extending in an axial direction thereof;     -   the outer circumference of each of the bulges (3) is bent into         the shape of waves in an axial cross-section;     -   each top portion (9) of the wave touches the inner surface of         the outer pipe (2) at the outermost end of the bulge (3) in the         radial directions in an axial cross-section;     -   the axis lines of the outer pipe (2) and the inner pipe (1) are         bent in the state where the outer pipe (2) is fitted outside the         inner pipe (1);     -   a first fluid (4) flows in the inner pipe (1); and

a second fluid (5) flows between the inner pipe (1) and the outer pipe (2).

The present invention according to claim 2 is a double pipe heat exchanger according to claim 1, wherein only the center portions of the end edges of the balloon-shaped bulges (3) on the outside in the radial directions touch the inner surface of the outer pipe (2).

The present invention according to claim 3 is a double pipe heat exchanger according to claim 1 or 2, wherein:

-   -   opening rims (6) at both the ends of the inner pipe (1) in the         axial direction are connected and fixed to the inner surface of         the outer pipe (2) all around the rims;     -   a pair of ports (7) for the first fluid (4) is provided on the         outer surface at both the ends of the outer pipe (2);     -   flanges (8) for connection are protrusively attached to both the         ends of the outer pipe (2); and     -   the double pipe heat exchanger is used as an EGR cooler wherein         the exhaust gas of an engine flows as the first fluid (4) and         cooling water flows as the second fluid (5).

The present invention according to claim 4 is a double pipe heat exchanger according to claim 1 or 2, wherein:

-   -   opening rims (6) at both the ends of the inner pipe (1) in the         axial direction are connected and fixed to the inner surface of         the outer pipe (2) all around the rims;     -   a pair of ports (7) for the first fluid (4) is provided on the         outer surface at both the ends of the outer pipe (2);     -   flanges (8) for connection are protrusively attached to both the         ends of the outer pipe (2); and     -   the double pipe heat exchanger is used as an oil cooler wherein         one of the first fluid (4) and the second fluid (5) is cooling         water and the other is oil.

The present invention according to claim 5 is a double pipe heat exchanger according to any one of claims 1 to 4, wherein, in an axial cross-section of the inner pipe (1):

-   -   the three balloon-shaped bulges (3) communicate with one another         in the center; and     -   the whole appearance of the inner pipe (1) is formed into the         shape of a three-leaf clover.

The present invention according to claim 6 is a method for producing a double pipe heat exchanger according to any one of claims 1 to 5, comprising the processes of:

-   -   inserting the inner pipe (1) into the outer pipe (2) and         bringing the top portions (9) of the waves of the bulges (3) of         the inner pipe (1) into contact with the inner surface of the         outer pipe (2) while keeping each of the axis lines straight;     -   welding only the opening rims (6) at both the ends of the inner         pipe (1) in the axial direction to the outer pipe (2); and     -   successively applying external force to the inner pipe (1) and         the outer pipe (2) and bending the whole body so as to bend the         axis lines of the pipes.

A double pipe heat exchanger and a production method thereof according to the present invention are configured as stated above and exhibit the following effects.

A double pipe heat exchanger according to the present invention is: formed by bending the inner pipe 1 and the outer pipe 2 in the state where the outer pipe 2 is fitted outside the inner pipe 1; and, in the state, configured so that the inner pipe 1 may have a plurality of bulges 3 and the top portions 9 at the outermost ends of the waves formed on the bulges 3 may touch the inner surface of the outer pipe 2. Hence, it is possible to: smoothly curve the axis lines of the inner pipe 1 and the outer pipe 2 in the state of keeping the cross sectional shapes of the inner pipe 1 and the outer pipe 2; and realize a highly accurate double pipe heat exchanger.

Further, the inner pipe 1 has a plurality of bulges 3 extending in the radial directions from the center, the bulges 3 communicate with one another, and a plurality of grooves 10 is formed at the outer circumference of the center portion. Hence, the effects that the heat transfer area increases, agitation is caused by the wavy surfaces of the bulges 3, and thus the heat exchange can be accelerated are exhibited.

Yet further, the cross section hardly deforms when the inner pipe 1 and the outer pipe 2 are bent by applying external force. That is, since the top portions 9 of the waves of the inner pipe 1 touch the inner surface of the outer pipe 2, the top portions 9 support the outer pipe 2 in the event of plastic deformation. Resultantly, a specific bush or the like is not required at deforming and bending can be applied.

Furthermore, the bending can be facilitated. Then the outer circumference of each of the bulges 3 is bent in the shape of waves in an axial cross-section and the top portions 9 of the waves touch the inner surface of the outer pipe 2 at the outermost ends of the bulges 3. Hence, the flow channel of the second fluid 5 is not segmented and thus it is possible to sufficiently agitate the second fluid 5 and accelerate the heat exchange.

In addition, it is possible to provide a double pipe heat exchanger having a simple structure and being excellent in heat exchange performance.

In the above configuration, a double pipe heat exchanger wherein only the center portions of the end edges of the bulges 3 on the outside in the radial directions touch the inner surface of the outer pipe 2 can further smoothen the flow of the second fluid 5 and accelerate the heat exchange. That is, the second fluid 5 can flow nearly all around the outer circumference of the bulges 3.

Next, with a double pipe heat exchanger wherein the opening rims 6 at both the ends of the inner pipe 1 are connected and fixed to the inner surface of the outer pipe 2 all around the rims, the flanges 8 are protrusively attached to both the ends of the outer pipe 2, and the heat exchanger is used as an EGR cooler wherein an exhaust gas and cooling water flow, it is possible to: facilitate the attachment of the EGR cooler to pipes; and provide an EGR cooler contributing to space-saving.

Further, when a double pipe heat exchanger of the same configuration is used as an oil cooler to cool oil with cooling water, it is possible to provide an oil cooler conforming to various pipes and flow channels and contributing to space-saving.

In the above configuration, by forming the appearance of the inner pipe 1 into the shape of a three-leaf clover in a cross section of the inner pipe 1, it is possible to provide a heat exchanger that: allows the second fluid 5 to flow uniformly at each part of the outer circumference of the inner pipe 1; and exhibits high heat exchange performance. Besides, it is possible to: bring the outer circumference of the inner pipe 1 into contact with the inner circumference of the outer pipe 2 in a balanced manner; bend the integrated body of the inner pipe 1 and the outer pipe 2 while avoiding extraordinary deformation of the cross sectional shape of the outer pipe 2; and provide a high performance heat exchanger.

A method for producing a double pipe heat exchanger according to the present invention includes the processes of: inserting the inner pipe 1 into the outer pipe 2 while keeping the axis lines straight; welding only the opening rims 6 at both the ends of the inner pipe 1 in the axial direction of the axis line to the outer pipe 2; and successively bending the inner pipe 1 and the outer pipe 2 by applying external force. By so doing, it is possible to: provide a double pipe heat exchanger the whole body of which is curved without changing the cross sectional shapes of the inner pipe 1 and the outer pipe 2; and use the heat exchanger also as a part of piping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing the first production process of a double pipe heat exchanger according to the present invention.

FIG. 2 is a vertical sectional view of the substantial part showing the second production process of the double pipe heat exchanger.

FIG. 3 is a sectional view taken on line III-III of FIG. 2.

FIG. 4 is a perspective explanatory view of a double pipe heat exchanger completed through the third production process.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments according to the present invention will be described in reference to drawings.

FIG. 1 shows the first production process of a double pipe heat exchanger according to the present invention, and FIG. 2 shows the second production process thereof. Then FIG. 3 is a sectional view taken on line III-III of FIG. 2, and FIG. 4 shows a double pipe heat exchanger according to the present invention in the state of completion through the third production process.

The heat exchanger has an outer pipe 2 and an inner pipe 1 that is inserted into the outer pipe 2.

The inner pipe 1 is, except both the ends as shown in FIG. 1, bent and formed into the shape of a three-leaf clover in cross section and the bulges 3 of the clover shape are bent into the shape of waves extending in the axial direction. Then the maximum radius of the clover shape is equal to the inner radius of the outer pipe 2. Both the ends of the inner pipe 1 are formed into a cylindrical shape and the outer diameter is equal to the inner diameter of the outer pipe 2. Further, three grooves 10 are formed at the outer circumference of the inner pipe 1 at the center portion.

The bulges 3 are formed into the shape of an inflated balloon as it is obvious from FIG. 3 and they communicate with one another at the axis line (the center of the inner pipe 1). The width of each of the bulges 3 gradually increases up to the intermediate portion and then gradually decreases toward the tip thereof in the radius direction from the center of the inner pipe 1 to the outside. Then the inner pipe 1 is inserted into the outer pipe 2 so that only the top portions 9 at the tips may touch the outer pipe 2.

With regard to the outer pipe 2, as it is obvious from FIG. 1, a pair of flanges 8 is welded and fixed to both the ends of the outer pipe 2, a pair of ports 7 is provided at both the end portions in the axial direction, and the pipes 11 are protrusively attached there.

With regard to the inner pipe 1 and the outer pipe 2 thus produced, the inner pipe 1 is inserted into the outer pipe 2 in the state of keeping the axis lines straight. Successively, only the opening rims 6 at the ends of the inner pipe 1 are fixed to the opening ends of the outer pipe 2 by welding. On this occasion, the top portions 9 at the tips of the bulges 3 touch the inner surface of the outer pipe 2. The contact points of the top portions 9 are not bonded.

Successively, external force is applied from the outer circumference of the outer pipe 2 and the outer pipe 2 is bent together with the inner pipe 1 as shown in FIG. 4. On this occasion, the axis line is deformed in the state where the top portions 9 of the bulges 3 of the inner pipe 1 are supported by the inner surface of the outer pipe 2.

In that regard, the pipes are bent in the state where the top portions 9 of the bulges 3 shown in FIG. 2 touch the inner surface of the outer pipe 2 to prevent the shape of the cross section of the outer pipe 2 from being extraordinarily deformed. Thereby, the whole body is bent as shown in FIG. 4, for example. The shape of the bending is formed so as to conform to the installation route of piping.

A double pipe heat exchanger thus bent is connected through flanges 8 as a part of the outlet pipe for the exhaust gas of an engine. Then cooling water as the second fluid 5: flows in from one of the pair of pipes 11; flows between the inner pipe 1 and the outer pipe 2; and flows out from the other pipe 11. Meanwhile, an exhaust gas as the first fluid 4 flows in the inner pipe 1 and the exhaust gas is cooled with the cooling water. The exhaust gas flows snakily in the bulges 3 where the exhaust gas flows comparatively easily. Likewise, the cooling water also flows snakily on the outside of the inner pipe 1. At the same time, the cooling water flows along the grooves 10 at the center portion of the inner pipe 1.

Although descriptions have been made on the basis of an EGR cooler in the above embodiment, the double pipe heat exchanger can be used as an oil cooler in place of the EGR cooler. On this occasion, it is possible to: run oil between the inner pipe 1 and the outer pipe 2; and run cooling water in the inner pipe 1. Otherwise, it is also acceptable to: run the cooling water between the inner pipe 1 and the outer pipe 2; and run the oil in the inner pipe 1. 

1. A double pipe heat exchanger wherein: an outer pipe is fitted outside an inner pipe; in a cross section orthogonal to the axis line of the inner pipe, the inner pipe has a plurality of balloon-shaped bulges communicating with one another and extending in the radial directions from the center, and the width of each of the bulges is the largest at an intermediate portion between the center and the outside of the inner pipe in a radial direction and gradually decreases toward both the sides of the bulge in the radial direction; a plurality of grooves is formed on the outer surface side at the center portion of the inner pipe in the manner of extending in an axial direction thereof; the outer circumference of each of the bulges is bent into the shape of waves in an axial cross-section; each top portion of the wave touches the inner surface of the outer pipe at the outermost end of the bulges in the radial directions in the cross section; the axis lines of the outer pipe and the inner pipe are bent in the state where the outer pipe is fitted outside the inner pipe; a first fluid flows in the inner pipe; and a second fluid flows between the inner pipe and the outer pipe.
 2. The double pipe heat exchanger according to claim 1, wherein only the center portions of the end edges of said balloon-shaped bulges on the outside in the radial directions touch the inner surface of said outer pipe.
 3. The double pipe heat exchanger according to claim 1 or 2 in combination with an exhaust gas system of a vehicle internal combustion engine, wherein: opening rims at both the ends of the inner pipe in the axial direction are connected and fixed to the inner surface of the outer pipe all around the rims; a pair of ports for the first fluid is provided on the outer surface at both the ends of the outer pipe; flanges for connection are protrusively attached to both the ends of the outer pipe; and wherein the exhaust gas of the engine flows as the first fluid and cooling water flows as the second fluid whereby the heat exchanger functions as an EGR cooler.
 4. The double pipe heat exchanger according to claim 1 or 2 in combination with a lubricating oil circulation system of a vehicle internal combustion engine, wherein: opening rims at both the ends of the inner pipe in the axial direction are connected and fixed to the inner surface of the outer pipe all around the rims; a pair of ports for the first fluid is provided on the outer surface at both the ends of the outer pipe; flanges for connection are protrusively attached to both the ends of the outer pipe; and wherein one of the first fluid and the second fluid is cooling water and the other is an oil whereby the heat exchanger functions as an oil cooler.
 5. The double pipe heat exchanger according to claim 1 or 2, wherein the balloon-shaped bulges are three in number and, in an axial cross-section of said inner pipe: the three balloon-shaped bulges communicate with one another in the center; and the whole appearance of the inner pipe is formed into the shape of a three-leaf clover.
 6. A method for producing a double pipe heat exchanger according to claim 1 or 2, comprising: inserting the inner pipe into the outer pipe and bringing the top portions of the waves of the bulges of the inner pipe into contact with the inner surface of the outer pipe while keeping each of the axis lines straight; welding only the opening rims at both the ends of the inner pipe in the axial direction to the outer pipe; and successively applying external force to the inner pipe and the outer pipe and bending the whole body so as to bend the axis lines of the pipes. 